Our beauty lab checked the temperatures of 18 one-inch-wide flat irons, disqualifying any that either never reached their maximum or exceeded it (some did — by 40°F!). Irons that broke when drop-tested also got the boot. We evaluated the remaining 11, straightening frizzy, wavy hair swatches and putting them in a high-humidity, climate-controlled room. Testers also used the irons at home, rating how well they worked.